Xformer delta-delta with high leg situation, (irregular voltage)

[Burdaneta]

Okay, that's fine. But, you should not leave a system completely floating like that.

Is the equipment you'll be playing with okay with a corner-grounded power source?

What is your plan for addressing the floating system? The usual options are:
1. Grounding one 480v wire.
2. Ground detection method.
3. Neutral-point derivation.

now i have to analyze that, i don’t have that kind of experience but i sure read some information and apply the best option for this case.

 

[LarryFine]

X2-X3 and H2-H3 as well i think is little higher because X3 is a high leg, am i wrong assuming this?

You are. As I said in post #30, each line-to-ground voltage is completely irrelevant to the transformer.

Now, the line-to-line voltages may be wonky because it's a high leg, especially if it's an open delta.

A high-leg delta is merely a 240v 3-wire delta source superimposed on a 1ph 120/240v 3-wire source.

The only reason the high-leg is a higher voltage is because of the neutral chosen to be grounded.

 

[infinity]

X2-X3 and H2-H3 as well i think is little higher because X3 is a high leg, am i wrong assuming this?

I don't think that the high leg should influence these phase to phase voltages since it's just a center tap on one coil that creates it.

 

[LarryFine]

I don't think that the high leg should influence these phase to phase voltages since it's just a center tap on one coil that creates it.

Agreed. It may be possible to bring the three secondary voltages closer to being balanced (equal) by rolling the primaries (A to B, B to C, C to A) and measuring the voltages each time.

 

[Burdaneta]

Agreed. It may be possible to bring the three secondary voltages closer to being balanced (equal) by rolling the primaries (A to B, B to C, C to A) and measuring the voltages each time.

Now in lost sorry , there’s a way to do that on the xformer? I really like to get more balanced voltages on those H2-H3 for example looks like to me 502v is too high to be used on ATS and equipment with lv controls.

 

[LarryFine]

Now in lost sorry , there’s a way to do that on the xformer?

It would need to be done on the primary side of your transformer, anywhere from the circuit breaker that supplies it to its primary (X) terminals.

The idea is to see if you can align the highest source voltage with the lowest secondary voltage, which comes from manufacturing tolerances.

 

[Burdaneta]

It would need to be done on the primary side of your transformer, anywhere from the circuit breaker that supplies it to its primary (X) terminals.

The idea is to see if you can align the highest source voltage with the lowest secondary voltage, which comes from manufacturing tolerances.

By rolling you mean exchange the phases on X side to try match the voltages output on H side?

 

[wwhitney]

Agreed. It may be possible to bring the three secondary voltages closer to being balanced (equal) by rolling the primaries (A to B, B to C, C to A) and measuring the voltages each time.

Only if the transformer is non-ideal and one or two of the 3 sets of windings differs significantly from the others. [Edit: I see you addressed this in post #46, which I had missed.] Which might be true. But the voltage measurements in post #37 (which I assume are under no-load conditions) do not strongly suggest that.

I guess if the transformer is loaded unevenly, and you take measurements under load, then rolling the supply could help by matching the load imbalance to the supply imbalance.

Cheers, Wayne

 

[Burdaneta]

Only if the transformer is non-ideal and one or two of the 3 sets of windings differs significantly from the others. [Edit: I see you addressed this in post #46, which I had missed.] Which might be true. But the voltage measurements in post #37 (which I assume are under no-load conditions) do not strongly suggest that.

I guess if the transformer is loaded unevenly, and you take measurements under load, then rolling the supply could help by matching the load imbalance to the supply imbalance.

Cheers, Wayne

There’s no load at this moment in fact i dont even provide power trough the secondary side disconnect box, in reading the values from the xformer lugs directly, sorry for the stupid question guys but And of you can clarify to me what rolling means ?

 

[LarryFine]

By rolling you mean exchange the phases on X side to try match the voltages output on H side?

Yes. See post #44 again.

 

[wwhitney]

There’s no load at this moment in fact i dont even provide power trough the secondary side disconnect box, in reading the values from the xformer lugs directly, sorry for the stupid question guys but And of you can clarify to me what rolling means ?

I think Larry's suggestion is potentially useful (so to speak), but it's icing on the cake. You need to sort out your transformer connections and secondary grounding first.

Cheers, Wayne

 

[Burdaneta]

Yes. See post #44 again.

Alright got the idea now, there’s no problem to connect the high leg on another phase different to C? No phase rotation problem?
high leg phase C from my panel to phase C on transformer X3

 

[LarryFine]

And of you can clarify to me what rolling means ?

Let's say you're at the breaker feeding the transformer. Or, you can do it in the transformer itself..

Move the black wire to where the red is, the red to where the blue is, and the blue to where the black is.

You're not reversing the rotation, just feeding each primary from a different pair of phase wires.

 

[LarryFine]

Only if the transformer is non-ideal and one or two of the 3 sets of windings differs significantly from the others. [Edit: I see you addressed this in post #46, which I had missed.] Which might be true. But the voltage measurements in post #37 (which I assume are under no-load conditions) do not strongly suggest that.

I guess if the transformer is loaded unevenly, and you take measurements under load, then rolling the supply could help by matching the load imbalance to the supply imbalance.

I'm not suggesting any defects, just using tolerances to see if a minimal imbalance can be obtained.

 

[LarryFine]

By rolling you mean exchange the phases on X side to try match the voltages output on H side?

No, see above post.

 

[LarryFine]

Alright got the idea now, there’s no problem to connect the high leg on another phase different to C? No phase rotation problem?
high leg phase C from my panel to phase C on transformer X3

The transformer won't care about rotation or which is the high leg.

If the high leg wire is orange, then move wires around in the transformer.

 

[Burdaneta]

Let's say you're at the breaker feeding the transformer. Or, you can do it in the transformer itself..

Move the black wire to where the red is, the red to where the blue is, and the blue to where the black is.

You're not reversing the rotation, just feeding each primary from a different pair of phase wires

once i roll the phases on primary side i should do the same on secondary side? I mean if i get the voltage balanced

 

[Burdaneta]

The transformer won't care about rotation or which is the high leg.

If the high leg wire is orange, then move wires around in the transformer.

Yeah i put orange on the high leg as you can see on the pictures , i will do that right now

 

[LarryFine]

once i roll the phases on primary side i should do the same on secondary side? I mean if i get the voltage balanced

No, you'd only be undoing what you just accomplished.

Roll the wires once, take secondary L-L voltages, then do it again.

Use whichever connection provides the closest secondary voltages.

 

[LarryFine]

Yeah i put orange on the high leg as you can see on the pictures , i will do that right now

The transformer does not care which is the high leg, only your service does.

The only reason the transformer has a high leg terminal is because it has a neutral terminal.

Since you're using the high-leg secondary as your primary, ignore which line terminal is which.